Finding Cut Sets

As stated earlier, the fault tree is a model of the system fault state. There are qualitative and quantitative tools to evaluate the tree. Qualitative analysis of fault trees is conducted through the use of cut sets and simple Boolean algebraic manipnlation. Trees are quantified by applying probabilities or frequencies of occurrence of each event fault. The event faults are then combined through Boolean manipulation, and the top-event probabUity is determined. You may wish to review a math book and become familiar with Boolean algebra and probability theory. The U.S. Nuclear Regulatory Commission s Fault Tree Handbook (Roberts et al., 1981) and NASA s Fault Tree Handbook with Aerospace Applications (Stamatelatos et al, 2002) are excellent references as well. 

In Boolean algebra, the OR gate represents the union of two or more events. The AND gate represents the intersection of two or more events. 

The same expression in set theory is A is B union C (A = B U C). The overheated wire is stated as E AND F must occur for D to occur. Again, in Boolean algebra, 

System Safety Engineering and Risk Assessment A Practical Approach 

Fault Tree Analysis Module of ITEM Tool Kit (Item Software [USA] Inc.) SAPHIRE (formerly IRRAS, U.S. Nuclear Regulatory Conunission) Probabilistic Risk Assessment Workstation (Electric Power Research 

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